A violent father facing a custody battle with his ex-partner drugged his children and killed them before taking his own life, an inquest heard today.

Graham Anderson, 36, was found hanging in his bedroom while the bodies of Jack, 11, and three-year-old Bryn were found covered by duvets in their beds of their home in Tidworth, Wiltshire on September 1 last year.

A coroner said that it was likely Anderson had attempted to cut Jack's throat with a kitchen knife but had then most likely smothered him during a 10-minute terrifying struggle that was overheard by a neighbour.

Hours later Anderson, who had been jailed in 2011 for violence and possessing cocaine and had been accused by ex-partner Victoria Jones of beating her, smothered his younger son before hanging himself.

David Ridley, the Coroner for Wiltshire and Swindon, ruled that Anderson, who was heavily in debt and was known to have alcohol and drug problems, had taken his own life while Jack and Bryn had been unlawfully killed.

Anderson, a former lorry driver, was facing a court battle with Ms Jones for custody of Jack and Bryn. They were living with him having previously been staying with foster parents organised by Hampshire social services.

Nick Jones, the children's maternal grandfather, said that he believed Anderson killed the boys out of vengeance because his daughter had left him and he was "losing control".

"When we heard the news of what this man had done to our grandsons the world changed for us. It will not be the same again," he said.

"Our eldest daughter's life has been ruined and the knock on effect to our family is too difficult to describe."

Mr Jones, who was supported by his wife Kathryn, the boys' grandmother, added: "There is absolutely no mitigating circumstance for what he did. Who could actually want to take the lives of their own children?

"We have asked ourselves this question over and over since the events of last year. Our conclusion, it was an act of vengeance on our daughter Victoria.

"After being subjected to 10 years of domestic violence, suffering in silence, she was at last attempting to put her life back together after a turbulent two years following their separation.

"He was losing control and as we have heard was unable to manage his life, or be a responsible parent."

The inquest in Salisbury heard Anderson was facing eviction from his two-bedroom ground floor flat in Auchinleck House, on Sidbury Circular Road, for not paying the rent.

On the day he was due to hand back the keys their bodies were discovered by the letting agent as she showed a prospective tenant around the property.

Just 10 days before the grim find Anderson had been prescribed a two-week course of sleeping tablets by his GP having complained of problems sleeping due to the stress of the custody fight.

Anderson had a meeting on September 6 to discuss Ms Jones's visiting rights, which he may have believed was an attempt by her to win custody.

The inquest heard that Anderson could have killed Jack and Bryn and then remained in the flat for up to two days before taking his own life. He left a brief note saying that Ms Jones may want to collect the children's belongings.

Jack was last seen alive on the afternoon of Wednesday August 29 and in the early hours of the next day a neighbour was woken by banging and screaming and Jack repeatedly shouting "what are you doing to me?".

The coroner said he was satisfied that Jack died during this disturbance, adding: "The evidence points beyond reasonable doubt that a struggle occurred when the adult male attempted to cut Jack's throat with a kitchen knife."

Jack's younger brother was last seen alive on the afternoon of August 30 with his father at a chip shop near their home, while Anderson was last seen on the evening of August 31 by a neighbour. The coroner said he was satisfied Bryn was already dead by this point.

Sarah Dodman, who had been woken by Jack's screams, told the hearing: "I heard little bangs on the wall which sounded like the older boy was flailing about - he was screaming.

"I just can't really describe it, my stomach just clenched and I thought that's not right. I could hear the older boy screaming 'what are you doing to me?'.

"It was exceptionally clear and he must have done it four or five times. I did not hear another voice and he did not stop crying the whole time.

"I then heard a low voice, no shouting, and it went on for about five minutes.

"I could not make out any words spoken, just the murmuring of a deep voice. At that time the little one was just screaming, screaming and screaming.

"His screaming was drowning out what was going on with the other boy. The very specific words I heard are 'what are you doing to me?' and are absolutely burned into my brain and I will never forget that."

Post mortem examinations found that Anderson had died from hanging while the cause of his children's deaths was given as "unascertained but unnatural".

Both Jack and Bryn had traces of their father's sleeping tablets in their bodies, tests after their deaths revealed. Jack also had bruising to his arm which was suggestive of being gripped.

Pathologist Dr Amanda Jeffery said the most likely cause of the boy's deaths was smothering but said there was not enough evidence to support that conclusion.

"It is not unusual in cases of this nature to find that children have been given some sort of sedative drug, for example in this case zopiclone, in the hope of putting the child to sleep to some extent," she said.

There was also blood staining discovered on furniture, walls and clothing around the flat, which was found to be both Anderson's and Jack's. Jack's blood was also found on the handle of a 12.5cm long kitchen knife.

The inquest heard that Anderson had been released from prison in November 2011 having been jailed for assaulting a man he believed was in a relationship with Ms Jones, as well as possessing cocaine.

By that time Jack and Bryn had been placed with foster parents by Hampshire County Council's social services department.

However, upon Anderson's release from prison, he gained custody of Jack and Bryn and moved to the flat in Tidworth while Ms Jones, a binge drinker, remained in Andover.

Social workers made regular visits to see Anderson and his children.

A serious case review commissioned after the children's deaths made seven recommendations but found that "even with the benefit of hindsight it is clear that the events that resulted in the children's deaths could not have been predicted".

The report added: "Whilst father's violence towards mother had been identified the risks to the children were less tangible. None of the professionals involved with the family anticipated his actions. There is no evidence of physical abuse by father against the children prior to their deaths.

"No-one, including members of the family, anticipated his actions nor is there any substantive information to suggest that anybody could or should have anticipated the tragic outcome."

Ms Jones did not attend the two-day inquest.

Anderson's brother, Adrian Bernhard, said afterwards: "We as a family are still finding it hard to come to terms with what has happened.

"It has turned our lives upside down and I don't think they will ever be the same again. We are completely devastated by this tragic event.

"It has been only a year now but it feels like only yesterday and still the pain does not go away."

Detective Constable Chris Conway, who led the investigation, said: "It was a harrowing inquiry and it is clear from the inquest that Bryn and Jack died at the hands of their father.

"It is clear that Graham Anderson presented himself to the authorities as a caring and devoted father.

"Why Graham did what he did, only he will know but it is clear he had financial problems and had the threat of eviction looming over him.

"A custody review hearing was to take place on September 6, which may have had a bearing on matters and he may have considered that his custody of the children may have been brought into question.

"It is clear from the inquest that no one, including his family and the authorities, could have foreseen the actions of Graham Anderson."